Chloroflurocarbons (CFCs) apparently act to deplete the ozone layer in the stratosphere, yielding ecological damage. The amount of CFCs and ozone depletion potential can be reduced by using some water or CO.sub.2 as blowing agents, and the amount of CFC can be eliminated by using all water or CO.sub.2 blowing agents. Water reacts with isocyanate to yield substituted urea and gaseous CO.sub.2 : EQU H.sub.2 O+2RNCO.fwdarw.RN(H)--CO--N(H)R+CO.sub.2
The isocyanate reaction to carbodiimide also generates gaseous CO.sub.2 : EQU 2RNCO.fwdarw.RN.dbd.C.dbd.NR+CO.sub.2
However, it is known that the CO.sub.2 -blown foams shrink. In an article entitled "Novel Polyols for CFC Reduction" (M. Aoyagi et al., SPI ANTC (1980), pages 95-100), CO.sub.2 -blown foam which had passable dimensional stability in low temperature or high temperature accelerated aging tests showed large deformations after a certain passage of time when left at room temperature.
In another article entitled "Low Density Rigid Foam Without the Use of CFCs" (D. C. Krueger et al., SPI ANTC (1990), pages 90-94), a number of all water (CO.sub.2) blown urethane foams gave good room temperature dimensional stability but poor stability at elevated temperature. Shrinkage was especially pronounced at 158.degree. F./100% R.H.
In U.S Pat. No. 4,945,119, rigid closed cell urethane foams produced using 5 to 70 mole percent CO.sub.2 blowing gave cold shrinkage (-22.degree. F.) unless co-expanded with a low boiling cylindered gas (e.g., CFC-142b having a boiling point of 10.degree. C. or 263.8.degree. K.). A low boiling gas must be included so as to withstand the negative internal pressure from the departing CO.sub.2, otherwise shrinkage occurs. The use of low boiling gases will require that current foam producers purchase very expensive processing equipment. Most of the low boiling gases being considered, such as CFC-142b, are HCFCs. The Clean Air Act of 1990 moved up to the end of 1995 the deadline for the U.S. to cease production of CFCs and other ozone depleting chemicals. The HCFCs, such as CFC-142b, will be phased out in the 2015-2030 time frame, with current impetus to move this up. CFC-142b, for example, still has an ozone depletion level of 0.025, though this is lower than CFCl.sub.3 with an ozone depletion level of 1.0.
The three references cited above, whereby CO.sub.2 -blown foams are shown to shrink at room temperature, elevated temperature, and low temperature, show that shrinkage is a problem with CO.sub.2 -blown foams. Shrinkage is a problem because a freshly made foam containing CO.sub.2 in the cells rapidly loses this gas by outward diffusion, leaving a negative internal pressure and possible shrinkage. Conversely, the rate of diffusion of CFCl.sub.3 from a foam is almost negligible with much less chance of shrinkage.
In addition, water blowing yields high exotherm or heat of reaction. In the typical CFCl.sub.3 expanded urethane foam, the hydroxyl groups react with isocyanate in an exotherm reaction to give a peak exotherm temperature in the 280.degree.-320.degree. F. range. But in an all water blown foam, the water reaction with isocyanate is also exothermic, and adds to the heat generated and now liquids such as CFCl.sub.3 cannot be utilized to volatilize and dissipate some of the heat. So all water blown foams give much higher exotherm (e.g., in the 350.degree.-380.degree. F. range). At these high temperatures, foams can thermally split or scorch and char or even burst into flames, and some foams are even deformed and collapse at too high a temperature.